hi all,

Ive got an '89 f150, recently it has had an intermittently high idle. I was checking today for vacuum leaks and couldnt find any, so whilst running I disconnected the IAC valve, that made the idle drop back to about 600rpm, although the iac is fairly new could this mean that it is the iac valve that is faulty?

 

Could also be the TPS. Check the voltage range and make sure it's correct.

 

ok, will check that today. is there any harm that can be done by driving the truck with the IAC plug disconnected?